Breeding a Mare with Shipped Semen

– Often perceived as going to be difficult, this can be a simple matter with some careful preparation, awareness and communication!

By Jos Mottershead

There are probably two major keys to successfully breeding a mare with shipped semen – preparation and communication.

Breeding a mare with shipped semen - Normal epithelial cells in cytology

Normal non-inflammatory endometrial epithelial cells

Carefully preparing your mare, and the associated monitoring of her estrous cycle will hopefully result in a timely breeding. An endometrial swab should be taken, and a cytology smear made, with further diagnostics and/or treatment carried out if indicated (more information on this is available in our article about the importance of uterine cytology smears). It is essential that the mare’s estrous cycle be followed carefully, and ongoing follicular activity monitored (this is known as “following the follicle”) and recorded. In order to do this, a person experienced in palpation or ultrasound use is needed – most usually a veterinarian. Hormonal manipulation of the estrous cycle may also be called for, in order to pinpoint ovulation more easily or accurately. This is especially important if the stallion is not always available for collections – some stallions are not collected if they are showing; some farms will only collect on an every-other-day basis; and some farms will not collect on weekends. (For more information on monitoring estrus and hormonal manipulation, see our article on monitoring cycles).

This is where the “communication” aspect starts to come into play. Communicate with the farm where the semen will be collected. Make sure that you are aware of any limitations on collection BEFORE your mare is ready to be bred. Ask the farm if semen from the desired stallion is always available; ask if they have a preferred protocol for ordering semen – some farms require one to have called in the order no later than perhaps 10.00 am on the day the shipment has to be sent. Other farms may even require a call the evening before that. An added note concerning communication by the mare owner to the stallion farm – show consideration in the timing of your telephone calls! The farm manager – especially if it is a busy breeding farm – will be receiving many phone calls during the breeding season, in addition to completing the regular days work. I’m sure most managers will appreciate it if you make sure that you call at a civilized hour – so remember time zone differences!

Another point that can produce subsequent frustration is discovering that your foal is not eligible for registration by the Breed Registry because some important Registry requirement was overlooked: Does the Registry permit the use of shipped semen? Does it require a Veterinarian to perform the insemination, or if an A.I. Technician is permissible, must they be “approved” by the Registry? Are shipped semen permits required? Is the stallion required to be specially licensed? These are all items that should be checked out before your mare is bred, and is quite often most easily achieved by contacting the applicable Registry directly.

Once your mare enters her estrus phase (“heat”), it is often helpful to call the stallion farm to advise them of the fact. They will then be aware that they will probably need to be shipping semen to you within the next 3-5 days. If you have already had the mare palpated or ultrasounded at this stage, tell them the results. Follicular size will be a rough indicator for them as to how many more days before you will need semen – the follicle typically grows at between 3 and 5 mm per day, and is unlikely to ovulate prior to being 35 mm in diameter. Remember that although at this stage it seems as though your whole life is focusing around getting your mare bred, you may only be one of many mare owners contacting the stallion farm, and therefore they need to schedule their collections accordingly.

Make sure that your veterinarian and inseminator will be available whenever they will be needed. It’s no use having a mare ready to be bred and the semen in your barn if there’s no one available to inseminate! Likewise, if your mare is ultrasounded with a 3 centimeter follicle on a Friday, will your veterinarian be prepared to come out on Sunday to check the mare if the farm needs to know by Sunday night for a Monday collection and shipment?

Find out by what method of transport the semen will be shipped. Will it be a courier company, or a counter-to-counter airline shipment? If it’s a courier, find out if they will be able to deliver by a certain time of day (this usually depends on your location – some remote or cross-border locations are even a 2 day shipment, which will probably be useless for the semen). If you wish to pick up the shipment at the courier depot, it must be marked “hold for pickup”. Picking semen up often results in your being in possession of it sooner than if you wait for a delivery. If the semen is being shipped counter-to-counter by an airline in North America it is essential that the shipping farm has “verified known shipper status” with the airline being used. Without that status, due to security constraints, the semen will not be accepted for shipment. Also be aware that this status is not a blanket status for all airlines, but must be obtained separately from each airline used. Someone will also need to be available to pick it up at the airport. What time will it arrive, and when does the freight department close? Note too that if you are using different airlines in your counter-to-counter shipment, with a transfer in the middle, you will require someone to physically carry the container from one airline’s counter to the next – neither airline will be likely to provide that person – and that the person must have “verified known shipper status” in order for the shipment to be accepted by the second airline! Remember that if the semen is traveling between Canada and the US, not only will it have to “clear Customs” (CBSA), but also the agricultural (document) inspection by CFIA (so the required documents must also be present – see our article on Shipping Semen to Canada from the USA for more details) and there must be a officers present to do that. Many of the smaller International airports do NOT have Customs officers present around the clock of even in some cases CFIA officers available. For semen entering Canada, also remember that it is likely that you will be required to pay Canada Customs “GST” or “HST” on the value of the semen when it arrives and the shipment must be accompanied by a Customs Invoice and breeding contract to provide documentation of that value. If this is a repeat shipment and you have already paid the tax, make sure you take your receipt with you, as you are not required to pay the tax more than once if it is a repeat breeding on a mare that did not conceive.

If your semen is being shipped by one of the larger airlines or courier companies, get a Bill of Lading number from the stallion farm, and you can “track” your shipment over the Internet. (“Click” on the following company names to go to their tracking sites: FedEx; UPS to track courier shipments – other companies usually offer the same ability through their websites). This will enable you to find out when your shipment left the stallion farm, where it is en-route, and if it has been delayed. If you note that it is sitting a long time at one location, make sure that you contact the transport company immediately to find out if there is a problem. You can also provide your e-mail address to the stallion farm with a request that they enter it into the courier system in order for you to receive automated updates related to the shipment.

If you have any questions at any stage of the shipping or breeding process, do not hesitate to ask someone. Remember that the only stupid question is the one that’s not asked! If your mare ends up not pregnant as a result of some silly hitch that you weren’t aware of, you will be very annoyed with yourself!

So you have the semen, and you’re starting to breathe a sigh of relief! The inseminator is on their way, your mare is in flaming standing heat, and everything is looking good…. What should you do now? Well, whatever you do, DO NOT open the cooled semen shipping container! It should stay closed until immediately prior to the semen being removed for insemination. Avoid extremes of temperature for the semen container. If the weather is hot, keep it in a cool place; if cool, keep it in the warm. Have your mare in a stall, tail wrapped, and ready to be inseminated. Have a bucket of warm water ready, and sit and wait for your inseminator to arrive!

Breeding a mare with shipped semen - drawing up semen

Withdrawing the semen using aseptic technique

Once the inseminator does arrive, upon opening the container, make sure that they confirm the identity of the stallion whose semen it is! A competent and thorough semen collection facility will have sent a collection report with the semen that will identify the stallion. If the stallion is not identified in some way on the semen container, make a note of that on any registry AI report – it could save you, the mare owner, considerable grief if next year the foal’s DNA does not match the sire and dam! Other information that will be provided on paperwork by the responsible stallion operation may include the time the collection took place, the motility at that time and the number of sperm shipped, as well as the type of extender and antibiotic used. For imported semen, checking the import health documentation is also important. Once identification and paperwork is checked, ensure that the inseminator gently mixes the semen before they inseminate. Often the sperm will settle to the bottom of the package during shipment. All that is necessary is to invert the package three or four times before the semen is drawn into the insemination syringe. The type of syringe used is important too. Make sure it is an all-plastic syringe, without a rubber seal on the plunger such as is seen on regular syringes. It has been determined that standard syringes can be highly spermicidal with some stallion’s semen.

Modified rectal sleeve slide warmer

The rectal sleeve slide warmer

Once the mare is inseminated, or indeed, if you have enough assistance available before she is inseminated, a small sample of the semen should be evaluated to determine the sperm percentage progressive motility. Make sure that this sample is warmed prior to evaluation, as in the cooled state motility will be alarmingly reduced. If your inseminator does not have a slide warmer or incubator, a temporary one can be easily made using a bowl of warm water, and “cling film” kitchen roll, a Zip-Loc bag, or a rectal sleeve filled with warm water (see our description of making a temporary slide warmer). Using the information from the semen collection report that hopefully accompanied the shipment, multiply the total number of sperm shipped by the percentage of progressively motile sperm that you are now seeing (for more information on determining progressive motility, see our article entitled How Progressively Motile Are Those Sperm?”). Ideally you will want to have inseminated 500 million progressively motile sperm. The lowest number to be used for a dose before pregnancy rates start to drop is 100 million (see The Semen Looked Bad – Or Is It?). If the number is below that, notify the stallion farm of your concern, although don’t make a big deal of it at this stage, otherwise you may be in a happy but embarrassed position a couple of weeks later – and indeed, some wait until a negative pregnancy check has been obtained before approaching the stallion farm. If you do contact the stallion farm, make sure that the sample was mixed and warmed prior to proper evaluation, and several samples evaluated. It is very frustrating for the stallion manager to be told that the semen was not of an acceptable quality, only to find later that there was nothing wrong with the semen, but the evaluation was sub-standard!

One of the big debates when breeding a mare with shipped semen is whether to inseminate both doses at the same time if two are shipped, or whether to hold one until the following day. There are valid arguments to be made for both schools of thought, however there is a strong preponderance of scientific evidence to support holding the second dose for later insemination in most cases. Generally I will take action according to whether I feel confident that the mare will ovulate within the 24 hours after insemination or not and the number of progressively motile sperm present in the insemination dose upon receipt.

If I believe the mare is going to ovulate within the next 24 hours (which is certainly what we aim for), and if the progressive motility of a single insemination dose yields more than 100 million progressively motile sperm, then I will inseminate just a single dose. The greater the volume of the insemination dose, the greater the possibility that a mare with a delayed uterine clearance problem may be incapable of clearing it – more commonly older or multiparous mares. Hopefully a single insemination dose has been calculated to be 1 billion progressively motile, morphologically normal sperm at the time of shipment. That will then provide between 100 and 500 million progressively motile sperm by the time of insemination, presuming a 50% die-off rate in transit. As research has shown that inseminating greater numbers of sperm does not increase pregnancy rates1, there is nothing in my opinion to be gained, and yet much to be lost by inseminating both doses at once.

If I feel that the mare is not likely to ovulate within 24 hours, then I will retain the second insemination dose for use the next day – but this second insemination will not be performed until at least 24 hours after the first in order to avoid placement of sperm into a still-inflamed uterus. Research has suggested that sperm that are stored in extender rather than solely seminal plasma have an increased binding tendency to the inflammatory cells, therefore lowering pregnancy rates substantially2. Extended semen does usually contain seminal plasma, but it is diluted, so this effect, although not as pronounced as with all of the seminal plasma removed, is still apparent.

It is important to note that the post-breeding inflammatory response is a perfectly natural occurrence, and indeed is essential for the successful establishment of pregnancy under normal circumstances. When one looks at the mare’s perineum 12-16 hours after breeding and sees pus dripping from vulva, what is being seen is typically normal clearance of the post-breeding inflammatory response (not a “reaction to the extender”!) In susceptible mares however – usually, but not always, older or multiparous mares – the mare is unable to clear this fluid, and the result is subsequently an inhospitable environment in the uterus for the conceptus. As a consequence, the pregnancy is lost shortly after descent of the conceptus into the uterus about 5½ days after fertilization. This problem can usually be very easily, cheaply and successfully managed with the use of oxytocin in such a manner as is laid out in our article about oxytocin use in the mare during breeding.

One area that I very definitely feel is a false economy when breeding a mare with shipped semen is not following up with an ultrasound the day after breeding to make sure that the mare did indeed ovulate and that uterine fluid presence (post-breeding inflammatory response) is controlled. Some mares will “hold on” to the follicle just to prove everyone wrong! If the mare has not ovulated 48 hours after insemination, you should be considering obtaining another shipment for insemination as soon as possible.

The use of shipped semen is not complicated, and although there can always be unfortunate hiccups during the experience, if planning and communication are good, those errors will be kept to an absolute minimum and hopefully your shipped semen experience will be straightforward and successfully result in a pregnancy!


1: Squires EL, Brubaker JK, McCue PM and Pickett BW; Effect of sperm number and frequency of insemination on fertility of mares inseminated with cooled semen. Theriogenology 49:4; 743-749.
2: Alghamdi AS, Foster DN and Troedsson MHT; Equine seminal plasma reduces sperm binding to polymorphonuclear neutrophils (PMNs) and improves the fertility of fresh semen inseminated into inflamed uteri. Reproduction (2004) 127 593-600.

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